The invention relates to a method for regenerating a particle sensor, which comprises a ceramic base body, in the exhaust gas duct of an internal combustion engine for driving a motor vehicle, wherein a particle load of the particle sensor is determined by applying an electric voltage between at least two electrodes with interdigital arrangement, a temperature of the particle sensor is determined with a temperature sensor or meander mounted to the ceramic base body or from the electrical resistance of a heating element, and the particle sensor is regenerated by heating with the electrical heating element.
The invention further relates to a device for regenerating a particle sensor, which comprises a ceramic base body, in the exhaust gas duct of an internal combustion engine, wherein the particle sensor comprises at least two electrodes with interdigital arrangement for determining a particle load, a temperature sensor or meander mounted to the ceramic base body for determining a sensor temperature of the particle sensor and an electrical heating element for regenerating said particle sensor, and wherein an engine management system is provided for controlling the internal combustion engine and for acquiring and evaluating output signals of the particle sensor.
Legislative regulations stipulate the monitoring of the composition of the exhaust gas of internal combustion engines for compliance to limit values. Particle sensors are, for example, used to monitor particulate emissions of internal combustion engines and for the on-board diagnostics (OBD) within the scope of a functional monitoring of particle filters. In this regard, collecting, resistive particle sensors (particulate matter sensors or PM sensors) are known which evaluate a change in the properties of an interdigital electrode structure on the basis of particle deposits. Two or a plurality of electrodes can be provided which engage in one another in a comb-like manner. Downstream of the diesel particle filter, the exhaust gas of the internal combustion engine is thereby guided past the electrode structure by means of a double-walled protective pipe construction. Due to an increasing number of particles deposited on the particle sensor, the electrodes are bridged by the particles, which results in a decrease in electrical resistance with increasing particle deposit, in a decrease in impedance or in a change in a characteristic variable related to the resistance or the impedance, such as a voltage and/or a current. For evaluation purposes, a threshold value, for example a measurement current between the electrodes, is generally defined and the time up to achieving the threshold value is used as the measurement for the deposited particle quantity. The rate of change of a signal can also alternatively be evaluated during the particle deposition.
The German patent publication DE 101 33 384 A1 discloses a resistive particle sensor. The particle sensor is constructed from two comb-like electrodes which engage in one another and are at least partially covered by a capturing sleeve. If particles are deposited on the particle sensor from a stream of gas, this leads to a change in the impedance of the particle sensor which can be evaluated, and from which the quantity of deposited particles and therefore the quantity of particles carried along in the exhaust gas can be determined.
If the particle sensor is fully loaded, the deposited particles are burned off in a regeneration phase with the aid of a heating element integrated in the particle sensor. To this end, the ceramic base body of the particle sensor is heated up to a high temperature, whereby said base body is however susceptible to damage due to regional thermal shock which can result from adherent or impacting water droplets. A regeneration of the particle sensor can therefore only be initiated if it can be assumed that no water can reach the particle sensor. To this end, a heat quantity calculation is carried out in an engine management system associated with the internal combustion engine, and a dew point release is provided if no water is presumably to be expected. The underlying assumptions are thereby based on a typical maximum quantity of water in the exhaust gas system which typically occurs during cold starting.
Such a consideration does not include a case like driving through water in which the outlet of the exhaust gas system can lie below the water line and water can penetrate into the exhaust gas system or in which the exhaust gas system can be so greatly cooled down from the outside that the dew point of the gas mixture situated therein is undershot. Ingressed or condensed water is in fact expelled again by means of exhaust gases. After a detected water crossing, the point must however be initially reached where conditions again prevail in the exhaust gas system which are required for a normal dew point release via the thereby utilized pipe wall temperature models and heat quantity integrals in the engine management system.